U.S. Pat. application Ser. No. 5126 to Allen Latham, Jr. filed Jan. 22, 1979 describes a centrifuge for separating one or more components of blood into precise fractions.
In the Latham centrifuge, a flexible, disposable blood processing bag is mounted in a contoured processing chamber consisting of a pair of support shoes within the centrifuge rotor. The contoured chamber is designed to support the blood bag in a position whereby separated blood components traverse a short distance in the process of separation. A flexible diaphragm or displacer bag is also positioned in the blood processing chamber of the rotor in a complementary relationship to the flexible disposable blood bag. The flexible diaphragm can be moved to apply pressure to the disposable blood bag in response to the introduction or expulsion, respectively, of a displacement fluid while the centrifuge rotor is either rotating or stationary. Additionally, displacer fluid can be expelled by pumping blood into the flexible, disposable blood processing bag.
The support shoes are held in a closed position by a support shoe holder having two side walls with curved lips which extend around the side edges of the shoes and are intended to maintain the shoes in a fixed side-by-side relationship with one another.
In practice, however, it has been found that a holder of the type shown in the Latham centrifuge would have to be fabricated from very heavy and expensive materials in order to withstand the vast pressures generated while processing blood as the centrifuge rotates.
For example, as previously mentioned, in one application it is desired to express one of the separated blood components from the blood bag into a centrally located collection chamber. The pressure required to do this is directly propositional to the length of tubing from the blood bag to the point of collection multiplied by the centrifugal force. Thus, for a 5.45 inch rotor radius and a centrifuge rotating at a speed of 2000 r.p.m. a pressure of 42 pounds per in..sup.2 is generated inside the blood processing bag.
This force, which amounts to in excess of 4000 pounds for a 10 in..times.10 in. bag, tends to push the two shoes apart.
One solution of this problem was to provide a rigid angle iron bracket adjacent the support shoes and affixed to the rotor wall. Long wedges were then driven into the gap between the angle iron brackets and the shoes. This solution made installation of the blood processing bag and displacer bag into the separation chamber shoes very cumbersome. Furthermore, stroboscopic observation of the support shoes during routine separation procedures revealed that the two shoes still were forced apart by about 1/4 inch at the midpoint between the two wedges.
Accordingly, a need exists for a low cost apparatus and method for securing the separation chamber support shoes in a centrifuge which apparatus is easy to install and minimizes the stress on the support shoes.